1) Field of the Invention
The present invention relates to N-hydroxyalkyltrimellitimide esters and bis-(trimellitimide) esters, methods of making them, and polyesters or polyamides that can be modified with them to provide better heat resistance and mechanical properties. Specifically, the method of the present invention seeks to make N-hydroxyalkyltrimellitimide esters and bis-(trimellitimide) esters in one step. These products may then be reacted with polyester or polyamide to provide the desired properties mentioned above. With the present invention, N-hydroxyalkyltrimellitimide ester is made by charging into a reactor equimolar amounts of trimellitic anhydride and primary hydroxyalkylamine, primary carboxylalkylamine or primary carboxylarylamine, with an excess of alcohol or diol. Bis-(trimellitimide) ester is made by reacting two moles of TMA with one mole of a diamine of the formula H2N—X—NH2 with an excess of alcohol or diol; where X is an aliphatic, alicyclic, or aromatic group.
2) Prior Art
HETI TMA-Imide
Polyester, in which part of the monomers are replaced by N-hydroxyethyltrimellitimide (HETI) is reported to show increased heat resistance, hardness, and impact strength. The use of HETI in polyethylene terephthalate (PET) imparts superior mechanical properties and heat and fire resistance.
HETI is an imide prepared from trimellitic anhydride (TMA) and ethanolamine:
N-(Hydroxyethyl)trimellitimide possesses a primary hydroxyl group, and an aromatic carboxylic acid group. The aromatic imide group is known to be stable towards thermal and oxidative degradation. Generally, TMA and ethanolamine are reacted in a solvent at an elevated temperature and the product imide recovered by filtration. Methods vary depending on the specific reaction medium and the order of addition of the reactants (i.e., adding ethanolamine (sometimes referred to as monoethanolamine, H2N—CH2—CH2—OH) to TMA or treating an ethanolamine solution with TMA).
It is also known to produce trimellitimide esters by first producing the imide and then converting the imide to an ester. This imide ester may then be reacted with or into polyester. The following prior art documents have been identified relative to the N-hydroxyalkyltrimellitimide ester and bis-(trimellitimide) ester process.
U.S. Pat. No. 3,060,191 to Kolb et al is drawn to a process of making trimellitic imides by reacting trimellitic anhydride with monoethanolamine (MEA). This new imide structure has a carboxyl group. The imide undergoes esterification and polycondensation to form modified polyester used to make fiber.
U.S. Pat. No. 3,975,330 to Suzuki et al discloses a process for making an imide modified polyester resin. The imide contains carboxyl groups. Esters are not mentioned. This reference does mention blending imides with polyesters.
U.S. Pat. No. 4,245,086 to Uno et al discloses a process for making trimellitic imide by reacting trimellitic anhydride with a monoalkylamine such as MEA, in the presence of specified catalysts. Two examples also show the preparation of a modified polymer by reaction of a HETI pre-polymer with bis-β-hydroxyethyl terephthalate (i.e. the precursor to PET). These compositions contain only a small amount of PET (2-4%). All the imides formed under the production process outlined in this patent have carboxyl groups.
U.S. Pat. No. 4,910,290 to Tung et al discloses that mechanical and thermal properties of polyester can be improved by incorporating trimellitic imides therein. More specifically, the imide is copolymerized into the polyester as a monomeric repeating unit. This patent discloses first making a trimellitic imide, then making a PET oligomer, and then reacting the imide with the oligomer in a copolymerization process. The polyester comprises 5-80 wt. % imide. Examples show preparation of modified PET compositions by heating PET oligomer and hydroxyethyl trimellitic imide (HETI) in the presence of antimony catalyst. The modified polyesters had better thermal properties compared to the control PET as shown by higher glass transition temperatures.
U.S. Pat. No. 5,102,978 to Richard et al discloses a typical imide with carboxyl end groups. The imide can be blended with polyester to create desired properties. The polyester most frequently mentioned is PET. The imide can be an imide-containing diacid monomer or diester thereof. Specifically, Example 1 teaches terephthalic acid and ethylene glycol are first condensed to a PET oligomer (PET heel), and then you react trimellitic anhydride (TMA) with various diamines to create bis-(trimellitimide) diacids. These diacids are then reacted with or copolymerized with polyethylene terephthalate oligomers.
U.S. Pat. No. 5,182,392 to Tanisake et al discloses a process for producing a bis-(trimellitimide) having carboxyl end groups. No imide esters are disclosed and there is no disclosure for reacting the imide with polyester.
French patent 2,435,491 to Toyo Boseki discloses a process for preparing imides by reacting trimellitic anhydride with a monoalkylamine. The production of the imide is carried out in various solvents including ethylene glycol. However, there is no disclosure of this being an imide ester product.
French patent 2,376,136 discloses a process for reacting trimellitic anhydride with a monoalkylamine. Again, various solvents are mentioned, including ethylene glycol and diethylene glycol.
German patent 2,659,092 to Toyo Boseki likewise teaches reacting trimellitic anhydride with a monoalkanolamine. There is no disclosure of reacting the imide with polyester.
The prior art discloses making a functional (carboxyl or hydroxyl) trimellitimide, making polyester oligomers, and then copolymerizing the imide with the oligomers. The imides are typically in powder form and are not easily copolymerized with polyester. Furthermore, the imides react or condense with themselves and thus have a tendency to not totally react with the polyester.
In the prior art set forth above, there was a disclosure for making trimellitic imides, a disclosure of reacting such imides with polyester, but no disclosure of a one-step process for making the trimellitimide esters. There is a need to make N-hydroxyalkyltrimellitimide esters and bis-(trimellitimide) esters that are easily blended with and compatible with polyester. There is a need to make N-hydroxyalkyltrimellitimide ester and bis-(trimellitimide) ester modified polyester to provide better heat resistance and mechanical properties.